The size of an integer is platform-dependent, although a maximum
value of about two billion is the usual value (that's 32 bits signed).
64-bit platforms usually have a maximum value of about 9E18, except on
Windows prior to PHP 7, where it was always 32 bit. PHP does not support
unsigned integers. Integer size can be determined
using the constant PHP_INT_SIZE, maximum value using
the constant PHP_INT_MAX since PHP 5.0.5,
and minimum value using the constant PHP_INT_MIN since
PHP 7.0.0.

Warning

Prior to PHP 7, if an invalid digit was given in an octal integer
(i.e. 8 or 9), the rest of the number was ignored. Since PHP 7, a parse error
is emitted.

Integer overflow

If PHP encounters a number beyond the bounds of the integer
type, it will be interpreted as a float instead. Also, an
operation which results in a number beyond the bounds of the
integer type will return a float instead.

Converting to integer

To explicitly convert a value to integer, use either the
(int) or (integer) casts. However, in
most cases the cast is not needed, since a value will be automatically
converted if an operator, function or control structure requires an
integer argument. A value can also be converted to
integer with the intval() function.

If a resource is converted to an integer, then
the result will be the unique resource number assigned to the
resource by PHP at runtime.

When converting from float to integer, the number
will be rounded towards zero.

If the float is beyond the boundaries of integer (usually
+/- 2.15e+9 = 2^31 on 32-bit platforms and
+/- 9.22e+18 = 2^63 on 64-bit platforms other than
Windows), the result is undefined, since the float doesn't
have enough precision to give an exact integer result. No
warning, not even a notice will be issued when this happens!

Note:

As of PHP 7.0.0, instead of being undefined and platform-dependent, NaN and Infinity will
always be zero when cast to integer.

Warning

Never cast an unknown fraction to integer, as this can
sometimes lead to unexpected results.

User Contributed Notes 20 notes

Here are some tricks to convert from a "dotted" IP address to a LONG int, and backwards. This is very useful because accessing an IP addy in a database table is very much faster if it's stored as a BIGINT rather than in characters.

Keep in mind, PHP integer operators are INTEGER -- not long. Also, since there is no integer divide in PHP, we save a couple of S-L-O-W floor (<division>)'s by doing bitshifts. We must use floor(/) for $ipArr[0] because though $ipVal is stored as a long value, $ipVal >> 24 will operate on a truncated, integer value of $ipVal! $ipVint is, however, a nice integer, so we can enjoy the bitshifts.

Converting to an integer works only if the input begins with a number(int) "5txt" // will output the integer 5(int) "before5txt" // will output the integer 0(int) "53txt" // will output the integer 53(int) "53txt534text" // will output the integer 53

Be careful with using the modulo operation on big numbers, it will cast a float argument to an int and may return wrong results. For example:<?php $i = 6887129852; echo "i=$i\n"; echo "i%36=".($i%36)."\n"; echo "alternative i%36=".($i-floor($i/36)*36)."\n";?>Will output:i=6.88713E+009i%36=-24alternative i%36=20

<?php$ipArr = explode('.', $ipString);$ipVal = ($ipArr[0] << 24) + ($ipArr[1] << 16) + ($ipArr[2] << 8) + $ipArr[3] ;?>1. the priority of bit op is lower than '+',so there should be brackets.2. there is no unsighed int in PHP, if you use 32 bit version，the code above will get negative result when the first position of IP string greater than 127.3. what the code actually do is calculate the integer value of transformed 32 binary bit from IP string.

d_n at NOSPAM dot Loryx dot com13-Aug-2007 05:33Here are some tricks to convert from a "dotted" IP address to a LONG int, and backwards. This is very useful because accessing an IP addy in a database table is very much faster if it's stored as a BIGINT rather than in characters.

Note that the soft-typing of numbers in PHP means that some things become very difficult. For example, efficiently emulating the more common linear congruential generators (LCGs) for fast, deterministic, pseudo-randomness. The naive code to create the next value in a sequence (for power-of-2 values of $m) is:

$seed = ($seed * $a + $c) % $m;

...where $m, $a, and $c are values and data types carefully chosen such that repeating this operation will eventually generate every value in the range $0 to $m, with no repetition.

I can find no good commonly used LCGs which use PHP-compatible values. The LCG values used in by rand() in systems like Borland Delphi, Virtual Pascal, MS Visual/Quick C/C++, VMS's MTH$RANDOM, old versions of glibc, Numerical Recipes, glibc, GCC, ANSI C, Watcom, Digital Mars, CodeWarrior, IBM VisualAge C/C++, java.util.Random, Newlib, MMX... *all* fail when ported, for one of two reasons, and sometimes both:

- In PHP on 32 bit machines and all Windows machines, $m = 2^32 or larger requires UInt or even UInt64, or the result becomes negative.

- Large $a multiplied by an integer seed gets converted to a float64, but the number can be too long for the 53-bit mantissa, and it drops the least significant digits... but the LCG code above requires that the most significant digits should be lost.

These are two classes of problem to beware of when porting integer math to PHP, and I see no clean and efficient way to avoid either one.

So if designing a cross-platform system that must work in PHP, you must select LCG values that fit the following criteria:$m = 2^31 or less (PHP limitation). Recommend: 2^31.$a = Less than 2^22 (PHP limitation); $a-1 divisible by all prime factors of $m; $a-1 divisible by 4 if $m is. Recommend: 1+(4*(any prime <= 1048573)).$c = smaller than (2^53-($m*$a)) (PHP limitation); relatively prime with $m. Recommend: any prime <= 23622320123.

PHP offers a slew of built-in functions and automatic type-casting routines which can get pretty complicated. But most of the time, you still have to take matters into your own hands and allow PHP to do its thing. In that case, and something that has NOT been mentioned, is how to construct your code. To keep things simple, I divide all my scripts in half. The top half gives my scripts the "capability" they need, and the lower half is the actual code to be "run" or "executed".

$item_label = "Chicken";$item_price = .80; // per lb.$item_qty = 3.5; // lbs.calculate(); // set $item_totalecho itemToString(); // -> Chicken [price=$0.80, qty=3.5, total=$2.80]?>Note: All type-casting is done by PHP's built-in number_format() method. This allows our program to enter any number (float or int) on item price or quantity in the runtime part of our script. Also, if we explicitly cast values to integer in the capability part of our script, then we start getting results that may not be desirable for this program. For example, if in the calculate method we cast item_qty to integer, then we can no longer sell chicken by the pound!

This is probably very similar to the MS C bug which also treats -2147483648 as an UNSIGNED because it thinks it's out of the range of a signed int.

The problem is that the parser does not view "-x" as a single token, but rather as two, "-" and "x". Since "x" is out of the range of an INT, it is promoted to float, even though in this unique case, "-x" is in the range of an int.

The best cure is probably to replace "-2147483648" with "0x80000000", as that is the hexadecimal equivalent of the same number.

When doing large subtractions on 32 bit unsigned integers the result sometimes end up negative. My example script converts a IPv4 address represented as a 32 bit unsigned integer to a dotted quad (similar to ip2long()), and adds a "fix" to the operation.

If you need to convert a numeric string (or more to the point, an object that represents a numeric value) that is greater then PHP_INT_MAX, and you don't have GMP or BCMath installed, you can cast to float.

For example, when using SimpleXMLElement, you sometimes have to cast the extracted values, such as xml attributes, because they are returned as SimpleXMLElements and not their values' native types. While print() has no trouble with converting them, other functions, such as max(), might not.

But if you cast such a value with (int), and it is over PHP_INT_MAX, you will just get PHP_INT_MAX (and vice versa for negative numbers).

Integer arithmetic in PHP is more accurate than one might think. On a 32-bit system, the largest value that can be held in an INT is 2147483647.However, a FLOAT can accurately hold integer values up to 10000000000000.(this is because the significand precision of a double is 53-bits).